5-leaf springs are great - but might not be worth the additional money for most of our forum members.
Most cases, re-arching the springs is all you need.
I would recommend replacing the rear shackle bushings (fairly cheap to purchase and you have to remove them anyway). You will need a total of 8 bushing halves (about $6-7 (US) per side, at RockAuto.com).
Personally – I would not reuse the U-bolts, and it might be faster to cut them off than the extra work to remove existing U-bolt nuts.
If reusing the Iso-clamp system, then you need 4x of 4-3/8” long, 7/16”-20 thread and 3” circle (inner diameter) U-bolts.
If going to older style shock plates, then the U-bolts will need to be 7” long, ½”-20 thread and 3” circle (diameter) U-bolts, also 4x.
On either, the length doesn’t have to be exact – but needs to be somewhat close.
The front leaf spring bushings are a pain to press in/out, but rarely go bad. Look for any deep cracks or rubber separation. Minor cracks are OK.
If planning on re-arching existing springs yourself, you will also need a new center bolt (per side), new clips/clamps (helps keep leaves in place, and possibly new leaf liners (pads that go between leafs to keep the metal on metal squeak you hear when going over bumps). These parts can be bought at most auto part stores or online.
Lastly, if retaining the Iso-clamp system, I would recommend tossing the rubber pads and go with polyurethane – or even better, just get rid of the Iso-clamp system and replace with older shock plates. The ride will be so much better and that alone will raise rear of car about 1/2".
BudW